The progressive neurological disorder is caused when neurons that control movement die earlier than they should, Dr. Rodolfo Savica, assistant professor of neurology at Mayo Clinic, tells The Post.

The disease is characterized by symptoms — including tremors, stiffness and slowness — that come on gradually and typically start on one side of the body.

While roughly 1 million Americans have Parkinson’s, doctors are still unsure what causes it. When Ali was diagnosed, fans blamed his boxing career. But that’s not entirely correct. “People who have head trauma are at an increased risk of Parkinson’s disease,” Savica says, but trauma alone can’t cause Parkinson’s — there must already be an individual predisposition to the disease.

“This gene’s abnormality leads to changes in the way your brain processes dopamine,” says Baylor’s Dr. Joseph Jankovic. “It’s a very important gene mutation that gives us insight into the disease.”

As of now, no drugs exist to stop the brain degeneration that causes Parkinson’s disease.Shutterstock

Researchers hope their discovery will help understand the roughly 10 percent of Parkinson’s cases that are genetic — and, they hope, the cases that aren’t currently considered genetic.

But finding a cure is still far off. Current treatments are focused on alleviating symptoms. One surgical treatment, deep brain stimulation, implants electrodes in the brain to regulate nerves. While it’s shown to reduce symptoms, it’s not viable for all patients and doesn’t stop the disease’s progression.

New medications are being tested, as are new methods of taking them — the most recent is a dissolvable film, similar to a breath strip, that administers a drug that would otherwise be injected.

“Curing [Parkinson’s] is complex because it’s a disease that is slowly progressive,” Savica says. “We do not have any drugs that can stop the degeneration of the brain.”